1. Field of the Invention
The present invention relates to control of an image processing apparatus which reads an image of a document to be conveyed.
2. Description of the Related Art
Conventionally, in an image forming apparatus, there has been available a system referred to as “feeding-reading” in which a plurality of documents are set in an automatic document conveyance device and conveyed one by one, and the documents are read by an optical type reading apparatus fixed at a document reading position. In this system, a bar-like light source is used, and a reading line is set parallel to a longitudinal direction (main scanning direction), with the documents being conveyed in a direction (sub scanning direction) perpendicular to the reading line. Further, light is applied from the light source to an image surface of the document being conveyed. Reflection light when the image surface passes the reading line is received, and an image of the image surface is successively read.
Thus, when a document is conveyed obliquely, and an image thereof passes the reading line obliquely (which will be hereinafter referred to as skew feed), the image will be read obliquely. In the above image forming apparatus, when image formation is performed based on an image thus skew-fed, a defective image which is formed obliquely on a sheet may be produced.
To avoid production of such a defective image, there is a technique (See, for example, Japanese Patent Application Laid-Open No. 8-81089) in which two sensors are arranged in a document conveyance direction and in a direction perpendicular to the document conveyance direction in a document conveyance path, and inclination of a document is detected based on a signal indicating that the document has passed the sensors arranged at the respective positions to correct skew feed of the document.
In this method, a document conveyance speed of a conveyance roller pair, each driven independently, is controlled to correct the inclination of the document, so that it is possible to effect skew feed correction without temporarily stopping the conveyance of the document. Thus, as compared with other skew feed correction methods, it helps to enhance efficiency in document conveyance and to achieve a substantial improvement in terms of image forming speed.
Further, since a correction of high precision is difficult to perform with mechanical skew feed correction alone which is based on a difference in speed of the conveyance roller pair, there is available a technique in which digital image data read after the above correction is rotated to correct the inclination (See, for example, Japanese Patent Application Laid-Open No. 10-32682).
However, in the above described technique, the skew feed correction is divided into two phases, i.e., the mechanical correction based on the conveyance rollers and the software correction based on the read image data. Thus, it is necessary to provide the sensors for detecting inclination of the document at two positions on the document conveyance path, resulting in an increase in costs of the entire apparatus.